Lyons W.C. (ed.). Standard handbook of petroleum and natural gas engineering.2001- Volume 1
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Computer Applications
125
Pointer-Each value of
a
variable declared to be of a pointer type gives the
memory location of the element
to
which
it
points.
Statements.
A
Pascal statement may be shorter than or may continue over more
than one line, since
a
semi-colon separates statements. Reserved words are not
separated from statements; therefore the statement preceding the word END (see
later sections) requires no punctuation. END of the main program unit
is
followed by
a
period. Comment lines are included in the program by placing
them between the symbols
(*
and
*).
Statements may be simple (single) or
compound,
i.e.,
a series of simple statements joined together in
a
block which
is
introduced
by
BEGIN and completed by END.
Nonexecutable Statements
Program unit heading-Program, procedure, or function name; the forms are:
PROGRAM name (input file name(s), output file name(s));
whete one input and one output file name, designated as INPUT and OUTPUT,
are assigned
to
default devices. For example,
PROGRAM TEST(INPUT,OUTPUT);
PROGRAM EDITOR(EDFILE, INPUT,OUTPUT);
and
FUN(:TION name(parameter list:type,
. .
.):function type;
PROCEDURE name(parameter list:type,
.
.
.);
The
declaration \:4R preceding a variable name(s) in
a
parameter list allows
the sub-program
to
modify the value of the variable stored in memory; if there
is no VAR preceding a variable name, the sub-program is passed only the value
of the parameter at the time of calling and cannot modify the stored value
of
that variable in the calling unit, e.g.,
PROCEDURE SAMPLE(X:REAL; YCHAR);
PROCEDURE LOOP(VAR A,B,C:INTEGER; YCHAR);
FUNCTION CHECK(VAR NUM:REAL; VAR PNR:INTEGER):REAL;
FUNCTION
BOUND(TEMP:REAL):BOOLEAN;
In
standard Pascal, although only in a few implementations of the language, a
function or procedure name
may
also
be
a
parameter to
a
sub-program. The
constants, types, and variables used in
a
sub-program,
as
well as those in the
main program, must be declared (see following declarations).
Label declaration-Labels identify an executable statement which may then
be referenced
by
GOTO;
they may be
1-4
digits and must be declared by
LABEI,
unsigned integer(s);
For example,
LABEL
50,999;
126
Mathematics
Constant declaration-Must precede variable declarations and be of the form
CONST
constant name
=
value;
constant name
=
value;
etc.
For example,
CONST
PI
=
3.1415927;
FACT
=
TRUE;
PIPENUM
=
27;
MINDPTH
=
1500;
MAXDPTH
=
7500.0;
CLRRADS
=
.34;
Type
declaration-Must be placed after CONST sequence and before variable
declarations; used to define new (not predefined) data types either as a range
of values or as specific values within parentheses and to define arrays, records,
and files. User-defined scalar types are ordered in increasing left to right
sequence. For example,
TYPE
UNIT
=
(PIPE,COLLAR,MOTOR);
TEMP
=
ARRAY[1..34 OF REAL;
PREC
=
RECORD
ATP
=
ARRAY[1..50,1..10] OF CHAR;
TIME: REAL;
CRUNIT: UNIT;
PRSSR: REAL;
RUN: INTEGER;
END;
STACKPTR
=
TSTACKELEMENT;
STRING
=
PACKED ARRAY[ l..MAXLENGTH OF CHAR;
(*
may be predefined on some systems
*)
TSURF
=
0.30;
NODE
=
l..PIPENUM:
CSET
=
SET OF
'A'..'Z';
Variable declaration-Placed after TYPE statements and defines the type
of
each variable, array, and record used in the program unit, for example
NXTUNIT:
LOG:
COUNT
PTEMP:
PREVTEMP:
LETTER:
NAME:
RUNS:
NODE;
PREC;
INTEGER;
TEMP;
TEMP;
CSET;
ARRAY[l..PO] OF CHAR;
FILE OF PREC;
BEGIN-Introduces the executable statements in each block of statements.
Computer Applications
127
END-Completes the executable statements in each block; followed by a period
Executable
Statements
at the end of the main program.
Assignment statements-Assign values by numerical or character constants,
by expressions (see Table
1-29
for arithmetic and set operators), or by input to
variables, array elements, and fields
PIPENUM:
=
1;
MAXTEMP:
=
PTEMP;
LETTER:
=
[
1;
(*
the empty set
*)
NAME:
=
‘WELL
#l’;
Input/Output statements-Two boolean functions that are useful in input
processing are EOF, which is TRUE if the pointer is currently at the end of the
input file and FALSE otherwise, and EOLN, which is TRUE if the pointer is at
the end of the current input line and FALSE otherwise.
Table
1-29
Pascal
Operators
Operator Description Operand(s)
Type
Result
Type
.-
_-
+
-
div
I
mod
not
or
and
<=
-
-
<>
>=
<
>
in
Assignment
Addition
Set union
Subtraction
Set difference
Multiplication
Set intersection
Integer division
Real division
Modulus
Logical negation
Disjunction
Conjunction
Set inclusion
Less than or equal
Equivalence
Equality
Exclusive or
Inequality
Set inclusion
Greater than or equal
Less than
Greater than
Set membership
Any, except file
Integer or real
Any set type
Integer or real
Any set type
Integer or real
Any set type
Integer
Integer or real
Integer
Boo
I
e an
Boo
I
e an
Boo
I
e an
Any set type
Any scalar type
Boo
I
e an
Scalar, set, pointer
Boo
I
e an
Scalar, set, pointer
Any set type
Any scalar type
Any scalar type
Any scalar type
Left operand scalar
Right operand: set
with base type same
as left operand
-
Integer or real
Same as operand
Integer or real
Same as operand
Integer or real
Same as operand
Integer
Real
Integer
Boolean
Boolean
Boolean
Boolean
Boolean
Boolean
Boolean
Boolean
Boolean
Boolean
Boolean
Boolean
Boolean
Boolean
128
Mathematics
READ(variab1e list);-Stores each item of data in a location indicated by the
variable associated with it
READLN(variab1e list);-Causes input control to shift to the next line when
the end of the variable list or line of input is reached
WRITE(variab1e list);-Can also output a character string by placing it,
enclosed by single quotes, inside the parentheses; a field (a format for output)
may be assigned to a data item as
WRITE(SUM:5);
or, in the case of a real number, as
WRITE(X:
10:2);
specifying the total width and also the number of decimal places. If no field is
specified, a default width is assumed.
WRITELN(variab1e list);-Output shifts to the next line when the output list
has been completed
Some examples of Input/Output statements are:
WRITE(1,X);
WRITELN('J
=
',
ABSU):6);
WRITE(X
+
Y5:2);
READLN(X,Y);
READ( A,B,C,D)
;
If no other files are specified for input or output in the program heading,
the default files or devices (usually the keyboard and the printer or the screen)
are used. If other (declared) files are to be used, they must be prepared (see file
handling statements) and then specified in the input/output statements, as follows
WRITE(filename, variable);
READ(filename, variable);
For example,
WRITE(PFILE,PRSSR(I));
READ(TEMP,TFCT);
For details on file pointers, buffer variables, and GET and PUT operations, see
one of the advanced Pascal texts listed in the references.
File-handling statements-Every file, except the INPUT and OUTPUT files,
must be defined in a VAR statement that gives its name and type, e.g.,
VAR
TEMP: FILE OF CHAR;
PRSSR: FILE OF REAL;
and must be prepared before data can be written to or read from that file.
REWRITE(fi1ename);-Produces
an empty file, to which data can be
written, and
Computer Applications
129
WRITE(filename, a,b,c,d);
can then write four items
to
the file.
RESET(fi1ename);-Prepares
a file for reading, beginning with the first item
READ(filename,X);
in the file, and
can then read the first item from the file.
Control statements-Affect the flow of statement execution within a program
unit (see subprogram statements below for passing of control between units).
The only general control statement in Pascal (which is rarely needed) is:
specified line number.
GOT0 line number;-Shifts control
to
the statement beginning at the
Conditional statements may be nested with other conditional statements and/
or with iterative statements. They are:
IF boolean statement THEN statement-Where statement may be a simple or
a compound statement (for boolean and relational operators, see Table 1-29)
and
IF boolean statement
THEN statement
1
ELSE statement 2-where the statements are as defined above
For example,
IF (PRSSR
<
MINP) OR (PRSSR
MAXP) THEN
BEGIN
X(P1PENUM:
=
PREVX;
CORRPR( PRSSR,X( PIPENUM),AVT)
END
ELSE
PREVX:
=
X(IP);
and
CASE selector expression
OF
label: statement;
label: statement;
label: statement
...
END
where, when the selector expression is evaluated, producing an ordinal value,
the statement following the label value which matches the selector expression
is executed, e.g.,
CASE PIPENUM OF
1:
PREV:
=
FALSE;
MAXP:
NEXT
=
FALSE
END:
130
Mathematics
Iterative statements control how many times a simple statement or a com-
pound statement is repeated, and also may be nested with conditional and/or
other iterative statements. They may be
WHILE boolean expression DO
statement
or
REPEAT
UNTIL boolean expression
statement
or
FOR variable:
=
expression TO expression DO
statement
where the variable and expressions must be of ordinal (not real) type and
TO
may be replaced by DOWNTO. In all types of iterative constructions, statement
may refer to a simple statement or to a compound statement introduced by
BEGIN and completed with END, for example,
WHILE NOT EOF DO
BEGIN
I:
=
0;
REPEAT
I:
=
I
+
1;
READ(TEMP( I))
UNTIL I
>
MAXI
END;
BEGIN
FOR I:
=
MAXI DOWNTO MINI DO
X(1):
=
FNC(X(1
-
1)
*
ABS(Z);
IF X(1)
>
XFT THEN AGSTP(X(I),I,PTP(I))
END;
Subprogram statements-Used to transfer control between program units-the
main program, functions, and procedures. A
function
call
is the invocation
of
a
function name in an assignment statement, such as
X:
=
DEF(Y)*Z;
which will transfer control
to
DEF and pass the variable Y to that function.
Control returns
to
the calling unit when the END statement of the function is
encountered. Intrinsic functions, supplied in the system library, are called in the
same manner. (See Table
1-30
for
a
list of standard Pascal intrinsic functions.)
A
procedure call
is made by stating the name of the procedure and the variables
to
be passed, e.g.,
CALCPRSSR( PIPENUM,TEMP,FFACTR);
will transfer control
to
procedure CALCPRSSR. Control returns to the calling
unit when the procedure END statement is found.
Computer Applications
131
Table
1-30
Pascal Intrinsic Functions
ABS
ARCTAN
CHR
cos
EOF
EXP
LN
ODD
ORD
PRED
RESET
REWRll
ROUND
SIN
SQR
SQRT
succ
TRUNC
-E
Returns the absolute value of an argument
Returns the arc tangent
of
an argument
Returns a character in the position in the collating sequence given by the
argument
Returns the cosine of an argument
Returns TRUE
if
the end of file has been reached, otherwise returns
FALSE
Returns the exponential e raised to the power of the argument
Returns the natural logarithm of an argument
Returns TRUE
if
an integer argument is odd, otherwise returns FALSE
Returns the ordinal number of an argument
Returns the predecessor to an ordinal argument
Initializes an input file
to
accept values
Initializes an output file
to
accept values
Converts a real argument
to
an integer value by rounding
Returns the sine
of
an argument
Returns the square of an argument
Returns the square
root
of
an argument
Returns the successor of an ordinal argument
Converts a real argument
to
an integer value by truncating
System Software
System software is the connection between the user and the machine. It
provides management
of
the system resources and utilities which simplify
development of applications programs. Essential system software includes
1.
Translators-Assemblers, interpreters, and/or compilers that translate
symbolic language into machine code.
2.
Linkers and loaders-Linkers resolve references between program units and
allow access to system libraries; loaders place code into the main memory
locations from which it will be executed.
3.
Operating systems-Manage hardware resources of the computer system.
Utili~ation may be of the
batch
method, in which program units, libraries,
and data are submitted to the system along with the
job
control language
statements needed to run the program. The operating system allocates the
central processing unit to one batch job at
a
time, according to
a
hier-
archical system.
Time-sharing
systems provide interactive sharing of resources
by many users. The system must interweave allocation of resources
to
users
and manage memory locations.
4.
Utility programs-Simplify use by performing particular tasks for the
programmer, such
as
editing, debugging, etc.
5.
File manager systems-Maintain files and handle data input
to
and output
from the files.
Database management
systems
(DBMS)
contain integrated sets
of files related by their use and provide uniform software interfaces for
accessing data. The essential relationships between records in the files may
be of several types, including sequential, associative, or hierarchical.
6.
Telecommunications monitors-Supervise communications between remote
terminals and the central computer.
132
Mathematics
System
Hardware
System hardware consists of the central processor, the input devices (usually
a keyboard), the output devices (probably both a video display terminal and a
hardcopy printer), long-term storage devices, and perhaps communications
components. In smaller systems, more than one of these components may be
“built in” to one unit, while in larger systems there may be many units each of
several components associated with the system.
The
central processing unit
(CPLJ) consists of the arithmetic-logic unit
(ALU),
the control unit, and the central storage (short-term memory) unit. The CPU
is
normally classified by size of the word (number of bits in one piece of infor-
mation or address), size of memory (which is partly dependent upon the size
of the word available and is expressed in KB, i.e., kilobytes) and by speed of
operations (given in megaHertz, mH). There are many combinations of these
factors, depending upon the processor chip used and upon the architecture of
the machine. Speed of operation and
of
data transfer is of major importance
in large number-crunching programs. Memory size affects the size of the
program and the amount of data that may be held at one time, while word size
primarily affects the size of memory available.
A
useful addition to the system,
if a need for large-scale number crunching is anticipated, is the arithmetic co-
processor chip, which performs high-speed numerical operations.
Keyboards are the most widely used
input devices,
but optical scanners and
digital pads (for computer-aided design) are some additional input devices. Input
may also be from files stored on a disk or tape.
Video display terminals for output are available in several sizes (measured
diagonally in inches), various resolutions (number of pixels, an important factor
in graphics) and a choice of monochrome or color. The type of screen chosen
will depend upon the anticipated use. Hardcopy
output
devices
usually include a
printer, either a dot-matrix printer, in which the characters are formed by dot
combinations, or a laser printer. The number of dots per character unit
is
one
consideration in the quality of print in a dot-matrix printer, although options
such as double-strike may increase the print quality at the cost of speed. Speeds
of laser printers (as opposed to the larger line printers) are measured in pages
per minute (ppm), but the actual throughput on printers
is
not always a direct
correlation of ppm. Laser printers have become available at affordable prices
and have the major advantage of producing a much lower level of noise, as well
as of high-speed operation. For engineering and design use, plotters, either
black-white or multicolored are frequently added to the system. Output may also
be sent to a disk or tape for long-term storage.
Long-term memory storage devices
may be cassettes, for small amounts of storage
on personal computers, several sizes of floppy diskettes, hard (fixed) disks or
magnetic tapes (frequently used for duplicate “back-up” storage). This choice
can be based on the amount
of
available storage needed without changing
cassettes or floppy diskettes and on the speed of access to the device required,
with cassettes being the slowest and hard disks the fastest accessed devices.
Systems may also include
modems,
which connect small computers
or
terminals
to other computers or workstations either in-house or over telephone system lines
and whose speed of transmission is rated by
baud
(for binary information units,
the number of bits transmitted per second). Common baud rates for small
systems are
2400
or
9600
with higher rates possible. Computers may also be
networked together to share data or peripheral components such as high-
speed printers.
References
133
REFERENCES
General
1.
Marks’ Standard Handbook for Mechanical Engineers,
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T.,
Avallone, E. A., and Baumeister
111,
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Geometry
2.
Moise, E. E., and Downs, Jr.,
F.
L.,
Geometry,
Addison Wesley, Melano Park, 1982.
3.
Graening,
J.,
Geometry,
Charles E. Merrill, Columbus, 1980.
Algebra and Trigonometry
4. Benice,
D.
D.,
Precalculus Mathematics,
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5. Thompson,
S.
P.,
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Martin’s Press, New
6. Lial,
M.
L.,
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C.
D.,
Essential Calculus with Applications,
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7. Oakley, C.
O.,
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8. Thomas,
G.
B.,
and Finney, R.
L.,
Calculus and Analytic Geometry,
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York, 1984.
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Numerical Methods
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Numerical Methods,
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10.
Borse, G.
J.,
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and Numerical Methods for Engineers,
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Carnahan, B., Luther, H.
A.,
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O.,
Applied Numerical Methods,
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R.
W.,
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J.
C.,
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17.
Fox,
L.,
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de
G.
Allen,
D.
N.,
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C.,
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134
Mathematics
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G.,
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Statistics
23. McCuen, R. H.,
Statistical Methodr
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24. Gibra,
I.
N.,
Probability and Statistical Inference
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25. Kennedy,
J.
R., and Neville, A. M.,
Basic Statistical Methods
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26. Robbins,
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Zntroduction to Statistics, Science Research
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Statistical Methods,
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&
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Probability, Random Variables, and Stochastic Processes,
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SPE Microcomp News,
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Linger, R. C., Mills,
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I.,
Structural Programming: Theory
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=
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Schnider, G. M., and Bruell,
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C.,
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